My mom's been taking seroquel (quetiapine) every night for almost 16 years! will this have any effect on her?

It must be helping: Long-term risks include diabetes, increased triglycerides, increased cholesterol, fat deposition in the abdomen, and tardive dyskinesia, rarely tardive dystonia, or tardive akathisia.

I hope so: If she is taking it to prevent relapse for a mental condition that it is approved for (bipolar, schizophrenia, depression) i would hope that it has prevented a relapse. The question is what is it being used for, is she on the lowest dose needed to prevent relapse and has she suffered side effects from it? She should be monitored by an md who could answer these questions.